Field of the Invention
The present invention relates to a light-emitting device and an image forming apparatus.
Description of the Related Art
In recent years, image forming apparatuses have been developed which use, as exposure means, a line head with many organic electroluminescence elements (hereinafter, referred to as “organic EL elements”) disposed in one line. This line head includes the plurality of organic EL elements and a plurality of pixel circuits including transistors for driving these organic EL elements. The luminance of each organic EL element is controlled by controlling the amount of current to be flowed into the organic EL element by means of the corresponding pixel circuit.
Japanese Patent Application Laid-Open No. 2009-006718 discloses a line head using organic EL elements disposed in a line. The line head described in Japanese Patent Application Laid-Open No. 2009-006718 is such that a plurality of pixels disposed in a line are divided into a plurality of pixel blocks, and data signals are supplied in a time-division manner to pixel circuits connected to the pixels while the pixel blocks are sequentially selected by means of control signals from a shift register.
In Japanese Patent Application Laid-Open No. 2009-006718, the control signals for sequentially selecting the pixel blocks are each inputted as a common signal to all the pixel circuits in the pixel block. When the control signal is inputted into the pixel circuit at an end of the pixel block, the control signal travels through a control signal line and is inputted into the adjacent pixel circuit. The control signal is then inputted sequentially into the following adjacent pixel circuits, and the control signal is eventually supplied to all the pixel circuits in the pixel block.
Here, as the control signal travels through the control signal line, the waveform of the control signal is gradually deformed due to the parasitic impedance of the interconnection line such that the waveform is different between the first pixel circuit the control signal is inputted and the last pixel circuit the control signal is inputted. Such a difference influences the writing of a data signal to each pixel circuit and makes it difficult to accurately control the amount of current to be flowed into each organic EL element.
The influence of the deformation of the waveform of the control signal as described above occurs not only on light-emitting devices using organic EL elements but similarly on light-emitting devices using other light-emitting elements such for example as inorganic EL elements, e.g., light-emitting diodes (LEDs).